1. Field of the Invention
The invention relates to an input circuit for receiving an input signal in an integrated circuit. The invention also relates to a method for adjusting the operating point of an input circuit.
2. Description of the Related Art
Integrated circuits have input circuits for the purpose of receiving input signals. The input circuits assess the input signals with respect to a reference voltage that is usually prescribed externally. The external reference voltage is subject to fluctuations which stem from noise effects, signal cross-coupling or from simultaneous switching effects. The reference voltage deviates from its nominal value, in particular, when the integrated circuit is used in an overall system. These deviations result in the input circuit not being operated at its optimum operating point, thus adversely affecting the performance of the input circuit when receiving and assessing the input signal and adversely affecting the power consumption.
Conventional input circuits have a differential amplifier which is coupled to a current mirror such that the same current flows through both branches of the differential amplifier. One input of the differential amplifier is connected to the input signal and another input of the differential amplifier is connected to the reference voltage. However, if the reference voltages which are applied to one input of the differential amplifier differ, the optimum operating point is usually assumed only at the nominal reference voltage. If the applied reference voltage differs from the latter, the input circuit is not operated at the optimum operating point.
Therefore, there is a need for an input circuit which is intended to receive an input signal and can be operated in an optimum manner even when the applied reference voltage deviates. There is also a need for a method for adjusting the operating point of an input circuit.